This invention relates to the field of telephonic and other types of communication and data wire stripping tools. More particularly, this invention relates to a new and improved wire stripper particularly suited to the stripping of multiple conductor communication cable, which contains multiple twisted pairs of wire where each pair is jacketed together by a common layer of insulation.
Communication system and/or network efficiency is directly dependent upon the integrity of the connector scheme employed. Such connector schemes include, for example, standard interfaces for equipment/user access (outlet connector), transmission means (horizontal and backbone cabling), and administration/distribution points (cross-connect and patching facilities). Regardless of the type or capabilities of the transmission media used for an installation, the integrity of the wiring infrastructure is only as good as the performance of the individual components and cable that bind it together.
By way of example, a non-standard connector or pair scheme may require that work area outlets be rewired to accommodate a group move, system change, or an installation with connecting hardware and cable whose installed transmission characteristics are compatible with an existing application but are later found to have inadequate performance when the system is expanded or upgraded to higher transmission rates. Accordingly, connecting hardware and cable without properly qualified design and transmission capabilities, can drain user productivity, compromise system performance and pose a significant barrier to new and emerging applications.
Reliability, connection integrity and durability are also important considerations, since wiring life cycles typically span periods of ten to twenty years. In order to properly address specifications for, and performance of telecommunications connecting hardware and cable, it is preferred to establish a meaningful and accessible point of reference. The primary reference, considered by many to be the international benchmark for commercially based telecommunications components and installation, is standard ANSI/EIA/TIA-568 (TIA-568) Commercial Building Telecommunications Wiring Standard. A supplement Technical Systems Bulletin to TIA-568 is TIA/EIA TSB40 (TSB40), Additional Transmission Specifications for Unshielded Twisted-Pair Connecting Hardware and cable. Among the many aspects of telecommunications cabling covered by these standards are connecting hardware design, reliability and transmission performance. Accordingly, the industry has established a common set of test methods and pass/fail criteria on which performance claims and comparative data may be based.
To determine connecting hardware and cable performance in a data environment, it is preferred to establish test methods and pass/fail criteria that are relevant to a broad range of applications and connector types. Since the relationship between megabits and megahertz depends on the encoding scheme used, performance claims for wiring components that specify bit rates without providing reference to an industry standard or encoding scheme are of little value. Therefore, it is in the interest of both manufacturers and end users to standardize performance information across a wide range of applications. For this reason, application independent standards, such as TIA-568 and TSB40, specify performance criteria in terms of hertz rather than bits per second. This information may then be applied to determine if requirements for specific applications are complied with. For example, many of the performance requirements in the IEEE 802.3i(10BASE-T) standard are specified in megahertz (MHz), and although data is transmitted at 10 Mbps for this application, test "frequencies" are specified in the standard (as high as 15 MHz).
Transmission parameters defined in TSB40 for unshielded twisted pair (UTP) connectors include attenuation and near-end crosstalk (NEXT) and return loss.
Connector attenuation is a measure of the signal power loss through a cable and connector at various frequencies. It is expressed in decibels as a positive, frequency dependent value. The lower the attenuation value, the better the attenuation performance. Since connecting hardware is generally considered to be electrically short relative to the length of cabling between two active devices (i.e., up to 100 meters of cable is typically allowed), the attenuation performance of the connecting hardware is usually not a major performance consideration.
Connector crosstalk is a measure of signal coupling from one pair to another within a connector at various frequencies. Since crosstalk coupling is greatest between transmission segments close to the signal source, near-end crosstalk (as opposed to far-end) is generally considered to be the worst case. Although measured values are negative, near-end crosstalk (NEXT) loss is expressed in decibels as a frequency dependent value. The higher the NEXT loss magnitude, the better the crosstalk performance.
Connector and cable return loss is a measure of the degree of impedance matching between the cable and connector. When impedance discontinuities exist, signal reflections result. These reflections may be measured and expressed in terms of return loss. This parameter is also expressed in decibels as a frequency dependent value. The higher the return loss magnitude, the better the return loss performance.
Since most high speed transmission applications that are designed for use with twisted-pair cabling do not operate in a full duplex mode (i.e., transmit and receive signals are not carried over the same pair), the effects of signal reflections, as caused by connectors, are generally not significant with respect to the ability of the twisted pair cabling to support existing applications that are designed for use with twisted pair cabling. However, for future high speed applications that may employ full duplex transmission, connector and cable return loss pose a significant limitation unless properly controlled.
The net effect of these parameters on channel performance may be expressed in signal-to-noise ratio (SNR). For connecting hardware and cable, the parameter that has been found to have the greatest impact on SNR is near-end crosstalk.
Several industry standards specifying multiple performance levels of UTP cabling components have been established. For example, Category 3, 4 and 5 cable and connecting hardware are specified in EIA/TIA TSB-36 & TIA/EIA TSB40 respectively. In these specifications, transmission requirements for Category 3 components and cable are specified up to 16 MHz. They will typically support UTP voice and IEEE 802 series data applications with transmission rates up to 10 Mbps, such as 4 Mbps Token Ring and 10BASE-T.
Transmission requirements for Category 4 components and cable are specified up to 20 MHz. They will typically support UTP voice and IEEE 802 series data applications with transmission rates up to 16 Mbps, such as Token Ring.
Transmission requirements for Category 5 components and cable are specified up to 100 MHz. They are expected to support UTP voice as well as emerging video and ANSI X3T9 series data applications with transmission rates up to 100 Mbps, such as 100 Mbps Twisted-Pair Physical Media Dependent (TP-PMD) and 155 Mbps a synchronous transfer for mode (ATM) applications.
In order for a UTP connector and cable to be qualified for a given performance category, it must meet all applicable transmission requirements regardless of design or intended use. The challenge of meeting transmission criteria is compounded by the fact that connector categories apply to worst case performance. For example, a work area outlet that meets Category 5 NEXT requirements for all combinations of pairs except one, which meets Category 3, may only be classified as a Category 3 connector (provided that it meets all other applicable requirements).
There is constant need to design even better and innovative cable for the telephonic and communication industry as the aforementioned discussion clearly indicates. Such a "state of the art" recently developed cable is represented typically by Belden Wire and Cable Company's "Belden.RTM. Data Twist 350 Twisted Pair" cables, U.S. patent application Ser. No. 08/032,149 filed Mar. 17, 1993. The design and manufacturing process of this cable allows stable electrical performance to 350 MHz, more than triple the verified frequency range of the EIA/TIA 568 Category 5 standard. This cable displays superior performance characteristics across the frequency range. Compared with the current Category 5 standard, impedance and structural return loss are improved up to 50%, while capacitance unbalance is enhanced by 400%. The new cable's stable performance across the frequency range assures satisfactory performance in all of today's current applications, as well as at extended frequencies which might result from future networking needs. A 35% improvement in Resistance Unbalance results in a significant improvement in signal integrity. In addition, a 5 % improvement in attenuation provides a stronger, more accurate signal with less energy being lost as it travels down the conductors within the cable. This new cable, further, has the advantage of (1) uniform conductor to conductor spacing, (2) uniform twisting of insulated conductors into pairs, and (3) assurance that the twists of the pairs will not loosen up during manufacture or installation.
This new Belden cable is produced such that there are four twisted wire pairs jacketed by a layer of insulation. The wire pairs are composed of the two conductors surrounded by insulation. The wire pairs are twisted about each other at varying "lays" or rates of twist. The unique feature of this cable is that one common piece of insulation surrounds both the conductors of each wire pair. Prior art cable on the market is composed of wire pairs where each conductor has its own separate individual layer of insulation. Use of this new cable requires the following operations in order to make efficient and speedy connections. In operation (1) the outer layer of insulation (that layer which encloses the four pair of conductors) must be removed. Once the desired section of outer insulation is removed, four wire pairs are exposed that require further operations prior to making the necessary connections. The four wire pairs are twisted in very specific and different lays and are also twisted around one another. Of course, this new cable can also be produced as two or three pair cable as well.
There are prior art wire strippers which can be used to remove the outer layer of insulation covering a four pair telephonic or communication wire. However, such prior art tools do not have any capability to straighten or flatten the pair of twisted cable or any means to sever the webbed insulation of the individual pair. To accommodate and work with newer cables such as the Belden type Data Twist 350 and the like, a new tool is needed.